The present invention relates to a motor-driven compressor.
A motor-driven compressor includes a metal housing accommodating a compression unit, which compresses and discharges refrigerant, and an electric motor, which drives the compression unit. A cover that defines an accommodation chamber is coupled to the housing. The accommodation chamber accommodates a motor driving circuit that drives the electric motor.
When the cover is made of metal, the overall weight of the motor-driven compressor increases. The use of a resin cover allows the motor-driven compressor to be lighter. However, a resin cover would transmit electromagnetic noise from outside the compressor to the motor driving circuit. In addition, electromagnetic noise from the motor driving circuit may leak out of the compressor through the resin cover.
Accordingly, in Japanese Laid-Open Patent Publication No. 2008-215236, a metal conductor (shield) is stacked on and fixed to a resin insulator. Electromagnetic noise from the exterior is blocked by the conductor and transmitted to a housing. This limits the electromagnetic noise that enters an accommodation chamber, which accommodates a motor driving circuit, through the insulator. In addition, electromagnetic noise from the motor driving circuit is blocked by the conductor and transmitted to the housing. This limits the leakage of electromagnetic noise from the motor driving circuit to the exterior through the insulator.
When the outer surface of the conductor is exposed, the ambient air may erode the conductor. Thus, an insulator (outer insulator) may be fixed to the outer surface of the conductor. The insulator covers the outer surface of the conductor so that the conductor is not exposed to the ambient air. Further, to insulate the motor driving circuit from the conductor, an insulator (inner insulator) may be stacked on and fixed to the inner surface of the conductor so that the insulator is located between the motor driving circuit and the conductor.
Molding may be performed to form such a three-layered cover including insulators fixed to the outer and inner surfaces of the conductor. Specifically, when a conductor is arranged in a mold, the mold is filled with molten resin at the inner and outer sides of the conductor. The molten resin is then hardened to form resin insulators that are stacked on and fixed to the inner and outer surfaces of the conductor. This forms the three-layered cover including insulators fixed to the outer and inner surfaces of the conductor.
When the cover is returned to room temperature after being molded, the conductor, the outer insulator, and the inner insulator undergo thermal contraction. Since the linear expansion coefficient of the conductor differs from that of the insulators, the degree of thermal contraction of the conductor differs from that of the insulators. The adherence between the conductor and the insulators may hinder smooth contraction of each layer. This may deform the conductor and insulators during the thermal contraction. As a result, the desired shape and dimensional accuracy may not be obtained with the cover.